Method for accessing a service unavailable through a network cell

ABSTRACT

A method performed by user equipment (UE) includes receiving a request to access a service unavailable through a first network cell associated with the UE, and receiving a message from an access device associated with the first network cell, wherein the message identifies a plurality of second network cells providing the service.

BENEFIT OF PRIORITY

This application is a continuation of U.S. patent application Ser. No.12/817,157 filed on Jun. 16, 2010, which is based on and claims thebenefit of U.S. Provisional Application No. 61/187,640, entitled “Systemand Method for Implementing Circuit-Switched Fallback,” the entirecontents of each of which is incorporated herein by reference in itsentirety.

BACKGROUND

The present disclosure relates generally to implementing fallback toenable user equipment to obtain service from a network cell notcurrently associated with the user equipment, for example,circuit-switched fallback, and, more specifically, to minimizing delayand improving reliability for circuit-switched fallback.

As used herein, the term “device” can refer to a mobile station (MS), auser agent (UA), or user equipment (UE), and can include electronicdevices such as fixed and mobile telephones, personal digitalassistants, handheld or laptop computers, smartphones, televisions andsimilar devices that have network communications capabilities. The termsmay also refer to devices that have similar capabilities but that arenot readily transportable, such as desktop computers, set-top boxes,IPTVs or network nodes. The term “UE” can also refer to any hardware orsoftware component that can terminate a communication session that couldinclude, but is not limited to, a Session Initiation Protocol (SIP)session. Also, the terms “user agent,” “UA,” “user equipment, “UE,” and“node” might be used synonymously herein. Those skilled in the art willappreciate that these terms can be used interchangeably.

A UE may operate in a wireless communications network that provideshigh-speed data and/or voice communications. The wireless communicationsnetworks may implement circuit-switched (CS) and/or packet-switched (PS)communication protocols to provide various services. For example, the UEmay operate in communications networks using different radio accesstechnologies (RAT), such as an Enhanced Universal Terrestrial RadioAccess Network (E-UTRAN), Universal Terrestrial Radio Access Network(UTRAN), Global System for Mobile Communications (GSM) network,Evolution-Data Optimized (EV-DO), 3GSM, Digital Enhanced CordlessTelecommunications (DECT), Digital AMPS (IS-136/TDMA), and IntegratedDigital Enhanced Network (iDEN), Universal Mobile TelecommunicationsSystem (UMTS), Enhanced Data rates for GSM Evolution (EDGE), GPRS/EDGERadio Access Network (GERAN), and/or General Packet Radio Service (GPRS)technology. Other wireless networks that UE may operate in include butare not limited to Code Division Multiple Access (CDMA), cdma2000,cdma2000 1×RTT, cdma2000 HRPD, WLAN (e.g. IEEE 802.11) and WRAN (e.g.IEEE 802.22). UE may also operate in fixed network environments such asexample Digital Subscriber Line (xDSL) environments, Data Over CableService Interface Specification (DOCSIS) cable networks, WirelessPersonal Area Networks (PAN), Bluetooth, ZigBee, Wireless MetropolitanArea Networks (MAN) (e.g., WiMAX, IEEE 802.20, IEEE 802.22 ethernet) oroptical networks. Some UE may be capable of multimode operation wherethey can operate on more than one access network technology either on asingle access network at a time or in some devices using multiple accesstechnologies simultaneously.

In wireless telecommunications systems, transmission equipment in a basestation transmits signals throughout a geographical region known as acell. As technology has evolved, more advanced equipment has beenintroduced that can provide services that were not possible previously.Such advanced equipment may include, for example, an evolved universalterrestrial radio access network (E-UTRAN) node B (eNB). Such advancedor next generation equipment may be referred to as long-term evolution(LTE) equipment, and a packet-based network that uses such equipment canbe referred to as an evolved packet system (EPS). As used herein, theterm “access device” will refer to any component, such as a traditionalbase station, eNB, or other LTE access devices, that can provide UE withaccess to other components in a telecommunications system.

The different networks described above provide a variety of services toconnected UE. Some networks, for example, provide only PS services andcannot provide CS voice or other CS domain services. As such, UE may beconfigured to connect to different types of networks to access both PSand CS domain services. For example, if UE is connected to a firstnetwork cell that does not provide CS domain service, the UE may beconfigured to implement CS fallback to connect to an accessible networksuch as a GERAN or UTRAN to access voice or other CS domain servicesprovided by those networks. As such, a CS fallback procedure allows UEconnected to a network using a first RAT and providing only PS domainservices to connect to another network using a second RAT and providingCS domain services. CS fallback may be used, for example, to initiatevoice calls via a cell of a network providing CS domain services, when,at the time of initiating the voice call, the UE was associated with acell of a network that only provides PS domain services. The UEinitiating the voice call may be either idle or active on the cell ofthe network that only provides PS domain services. In case the UE isidle it can be said to be camped on the cell and may be monitoring thepaging channel of that cell for paging messages for mobile-terminatedsessions or calls. In case the UE is active it may be communicating withthe cell and transferring data for a PS domain service.

FIG. 1 is an illustration of a CS fallback process wherein UE 10transitions from an E-UTRAN cell to a GERAN or UTRAN cell to access CSdomain services for initiating a voice call. In FIG. 1 , UE 10 isinitially connected to E-UTRAN cell 100. Because E-UTRAN cell 100 doesnot provide CS domain services, UE 10 implements CS fallback tocommunicate with the GERAN or UTRAN cell 102 to access CS domainservices. Depending upon network implementation, it is not necessarythat cells 100 and 102 be co-extensive. However, to transfer from onecell to another, UE 10 should be within the communication range of eachcell.

In FIG. 1 , UE 10 is first connected to or camped on E-UTRAN cell 100.To initiate a mobile-originated voice call, UE 10 transmits a signal 104to E-UTRAN cell 100 that includes a request to initiate a voice call.After receiving the request, E-UTRAN cell 100 transmits a signal 106 toUE 10 indicating that the voice call cannot be supported because E-UTRANcell 100 cannot provide the necessary CS domain services. Signal 106 mayalso include a reference identifying a candidate GERAN or UTRAN cell102, which does support the CS domain services for the voice call. Afterreceiving signal 106, UE 10 transfers to GERAN or UTRAN cell 102 usingthe information provided in signal 106. The transfer may be implementedusing a handover procedure, cell change order (CCO) procedure, PShandover procedure, or redirection procedure, for example. Note that inFIG. 1 , arrow 108 only indicates the transfer of UE 10's communicationfrom one cell to another, and does not indicate physical movement of UE10. After transferring to GERAN or UTRAN cell 102, UE 10 establishes aconnection for initiating the voice call as indicated by line 110. Inthe case of a mobile-terminated voice call, UE 10 may be first paged byE-UTRAN cell 100 for an incoming CS domain voice call. In response tothe page, UE 10 follows a similar process as described above for themobile-originated call to transfer to the GERAN or UTRAN cell 102 andafter transferring UE 10 responds to the page on the GERAN or UTRAN cell102.

To facilitate CS fallback, UE 10 may be configured to communicate withboth PS-based and CS-based networks. For example, UE 10 may supportcombined procedures for EPS/International Mobile Subscriber Identity(IMSI) attach, and Tracking Area update for registering with a MobilityManagement Entity (MME) to access PS domain services (for example, viaan E-UTRAN, UTRAN or GERAN access network) and for registering with aMobile Switching Center (MSC) to access CS domain services (for example,via a UTRAN or GERAN access network or another network supporting CSdomain services). The combined procedures also allow the MSC and MME tocreate an association between one another so that each is aware that UE10 is simultaneously registered with both the MSC and MME and that,therefore, the UE is registered with both the PS and CS networks.

When performing CS fallback, UE 10 may be in the best position todetermine which cell or cells are candidate cells to fallback to—UE 10can detect which cells are in close proximity or have particularlystrong received signal strength or quality (or other such preferentialparameters), and hence with which cells UE 10 would likely have asuccessful connection following the CS fallback process. As such, duringthe CS fallback process, UE 10 may undertake a measurement step todetect and identify the cells accessible to UE 10. In other words,before falling back to a cell providing CS domain services, UE 10 firstsearches for available candidate network cells via a measurementprocess.

The measurement step may involve interruptions in the downlink receptionand uplink transmission activities of UE 10 during which UE 10'sreceiver is temporarily retuned to the frequencies that might be used bythe candidate cells (e.g., in the case of GERAN candidate cells, thefrequencies on which broadcast control channels (BCCH) may betransmitted) that may be accessible to UE 10. These interruptions aretermed measurement gaps. The measurement gaps periodically occur. Onestandard currently defines 2 different periods: gap pattern 0, whichgives a 6 ms measurement gap every 40 ms, and gap pattern 1, which givesa 6 ms measurement gap every 80 ms. Thus the measurement gap patternsgive 7.5% (pattern 1) or 15% (pattern 0) of the UE 10's time to detectand perform measurements of cells of other networks, which thereforetake a relatively long time.

FIG. 2 is an illustration of an exemplary measurement gap pattern thatallows the receiver of UE 10 to be temporarily retuned to frequenciesthat might be used by GERAN cells to detect cells that are accessible toUE 10. At time t=0, RRC Connection Reconfiguration procedure isperformed to begin the measurement process. Periodic measurement gaps115 are then defined to allow UE 10 to perform measurements for GERANcells. During measurement gaps 115, UE 10 reconfigures its receiver inan attempt to detect and/or measure available candidate cells. In thenon-measurement gap periods 117, UE 10 assumes normal operation.

After the last measurement gap, sufficient measurements may have beenperformed by UE 10 and one or more candidate network cells that provideCS domain services may have been detected. UE 10 may then transmitmeasurement results to an access device of the PS network (e.g., anE-UTRAN eNB). The measurement results transmitted to the PS network maythen be used by the PS network to determine an optimal CS network cellto which UE 10 may be transferred during the CS fallback procedure.

When implementing CS fallback, delay is a concern. If UE 10 is initiallycamped on an E-UTRAN cell and wishes to access CS domain services, a CSfallback process may be executed. While the RRC (radio resource control)connection setup procedure of the CS fallback process may be relativelyshort (150 ms is the target time for the E-UTRA system design) themeasurement step and the step of selecting a target cell for CS domainservices can potentially take a significant amount of time. As such, CSfallback may be delayed resulting in delays in establishing the CSdomain services, possibly delaying the establishment of a voiceconnection for the user or negatively affecting other services accessedby UE 10. In particular, the need to carry out a number of steps whilecamped in E-UTRAN and possibly obtain system information for the targetcell may result in a delay which, to the user, is noticeably longer thanif UE 10 were initially camped on the target cell.

It is also possible that during CS fallback UE 10 may be directed to orselect a target cell that has (or, in other words, is in, or belongs to)a different location area (LA) than the cell with which or in which UE10 is currently registered. Any resulting location update may addfurther delay to establishing the CS domain service. Also, in amobile-terminated call, it is possible that the LA of the target cell isassociated with a different MSC from the MSC that handles the incomingcall. In that case, call establishment may fail.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of this disclosure, reference is nowmade to the following brief description, in connection with theaccompanying drawings and detailed description, wherein like referencenumerals represent like parts.

FIG. 1 is an illustration of a CS fallback process wherein UEtransitions from an E-UTRAN cell to a GERAN or UTRAN cell to access CSdomain services for initiating a voice call;

FIG. 2 is an illustration of an exemplary measurement gap pattern thatallows the receiver of UE to be temporarily retuned to frequencies ofother RATs (e.g., GERAN, UTRAN, or other CS networks) to detect networkcells providing CS domain services;

FIG. 3 illustrates a message sequence for implementing CS fallback whenUE camped on an E-UTRAN cell or other network cell wishes to initiate aCS voice call or use other CS domain services on another network cell;

FIG. 4 illustrates a message sequence for implementing CS fallback withthe addition of new signaling for transmitting idle mode measurementrequests and data between UE and the network;

FIG. 5 is an illustration of an exemplary measurement gap pattern thatimproves measurement efficiency:

FIG. 6 is an illustration of an alternative message sequence forimplementing CS fallback, wherein the alternative sequence eliminatessome of the communication steps between an access device and an MME;

FIG. 7 illustrates a communication flow diagram for implementing aUE-terminated call when Idle mode Signaling Reduction (ISR) is active:

FIG. 8 is an illustration of a network configuration wherein UE iscamped on an E-UTRAN cell and is also located close to the boundaries ofthe radio coverage of two GERAN cells;

FIG. 9 illustrates a conventional message flow for call setup on a CSnetwork for a UE-terminated call using the Stand alone Dedicated CHannel(SDCCH);

FIG. 10 illustrates a message flow for call setup on a CS network for aUE-terminated call using Fast Associated Control CHannel (FACCH)signaling;

FIG. 11 illustrates a wireless communications system including anembodiment of user equipment;

FIG. 12 shows a block diagram of user equipment including a digitalsignal processor (DSP) and a memory;

FIG. 13 illustrates a software environment that may be implemented by aprocessor of user equipment; and

FIG. 14 illustrates an example of a system that includes a processingcomponent suitable for implementing aspects of the present disclosure.

DETAILED DESCRIPTION

The present disclosure overcomes the aforementioned drawbacks and othersby providing a system and method for implementing fallback to enableuser equipment to obtain service from a network cell not currentlyassociated with the user equipment, for example, circuit-switched (CS)fallback, and, specifically, for minimizing delay and improvingreliability for CS fallback.

The various aspects of the disclosure are now described with referenceto the annexed drawings, wherein like numerals refer to like orcorresponding elements throughout. It should be understood, however,that the drawings and detailed description relating thereto are notintended to limit the claimed subject matter to the particular formdisclosed. Rather, the intention is to cover all modifications,equivalents, and alternatives falling within the spirit and scope of theclaimed subject matter.

As used herein, the terms “component,” “system,” and the like areintended to refer to a computer-related entity, either hardware, acombination of hardware and software, software, or software inexecution. For example, a component may be, but is not limited to, aprocess running on a processor, a processor, an object, an executable, athread of execution, a program, and/or a computer. By way ofillustration, both an application running on a computer and the computercan be a component. One or more components may reside within a processand/or thread of execution and a component may be localized on onecomputer or distributed between two or more computers.

The word “exemplary” is used herein to mean serving as an example,instance, or illustration. Any aspect or design described herein asexemplary” is not to be construed as preferred or advantageous overother aspects or designs.

Furthermore, the disclosed subject matter may be implemented as asystem, method, apparatus, or article of manufacture using standardprogramming and/or engineering techniques to produce software, firmware,hardware, or any combination thereof to control a computer- orprocessor-based device to implement aspects detailed herein. The term“article of manufacture” (or alternatively, “computer program product”)as used herein is intended to encompass a computer program accessiblefrom any computer-readable device, carrier, or media. For example,computer readable media can include but are not limited to magneticstorage devices (for example, hard disk, floppy disk, magnetic strips,and the like), optical disks (for example, compact disk (CD), digitalversatile disk (DVD), and the like), smart cards, and flash memorydevices (for example, card, stick, and the like). Additionally, itshould be appreciated that a carrier wave can be employed to carrycomputer-readable electronic data such as those used in transmitting andreceiving electronic mail or in accessing a network such as the Internetor a local area network (LAN). Of course, those skilled in the art willrecognize many modifications may be made to this configuration withoutdeparting from the scope or spirit of the claimed subject matter.

In general, the inventive system and methods have been developed toreduce the delay and improve the reliability of a CS fallback process.CS fallback may be implemented for transitioning from E-UTRAN to GERAN,specifically, or, more generally, from a first network that does notprovide CS domain services to a second network that does provide CSdomain services. For example, CS fallback may be implemented to allowfallback from E-UTRANs to UTRAN or CDMA2000 networks. To this end, thepresent system provides a more efficient measurement algorithm tominimize delay during the fallback procedure. The system may alsominimize communications that must be processed before CS fallback can becompleted. Although the following disclosure is primarily focused on asystem for implementing CS fallback from an E-UTRAN to a GERAN, thepresent disclosure applies to fallback between any combination of othernetworks such as E-UTRAN, WiMAX, UTRAN, CDMA2000 networks, or anynetworks.

When performing CS fallback, UE 10 may determine the most appropriate CSnetwork cell to connect to. Alternatively, the network (for example aneNB) may select the CS network cell that the UE should connect to basedon measurements of candidate cells provided by the UE. UE 10 can detectwhich CS network cells are in close proximity, and with which cells UE10 has the highest quality connection. During CS fallback, UE 10 mayundertake a measurement step to identify candidate cells accessible toUE 10, and search for available cells before transferring to a cellproviding CS domain services. The UE may, as part of the searchprocedure, identify cells that can provide those services or, based onpreviously received or configured information, search only for cellsknown to provide those services.

When implementing CS fallback, delay is a concern. If UE 10 is initiallycamped on a GERAN or UTRAN cell, for example, CS voice call signalingmay be started immediately. In contrast, if UE 10 is initially camped onan E-UTRAN cell, several additional steps (including steps 116-130illustrated on FIG. 3 ) may be performed. While some of these additionalsteps may be relatively short (for example, 150 ms is the target timefor the E-UTRA system design to establish an RRC connection), theinter-RAT measurement step (see step 124 of FIG. 3 ) and the step ofselecting the target cell for CS domain services (see step 130 of FIG. 3) can potentially take a significant amount of time. As such, CSfallback may be delayed resulting in delays in establishing the CSdomain services, possibly delaying the establishment of a voiceconnection or other service for the user.

Of additional concern, in conventional CS fallback processes, UE 10 maybe directed to or select a GERAN or UTRAN cell that has a differentlocation area (LA) from the cell with which UE 10 is currentlyassociated. In that case, UE 10 may perform a location area update afterarriving in the new cell before starting signaling related to the CScall. The location area update adds further delay to the CS domainservice establishment. Furthermore, in a mobile-terminated call, it ispossible that the new LA is associated with a different MSC from the MSCthat handles the incoming call. In that case, call establishment mayfail.

FIG. 3 illustrates a message sequence for implementing CS fallback whenUE camped on an E-UTRAN cell or other network cell wishes to respond toa paging request associated with an incoming CS voice call or other CSdomain service. Although FIG. 3 illustrates CS fallback from an E-UTRANto a GERAN, fallback to other networks supporting CS services such asUTRAN may be implemented using similar processes. Some differences inthe process of FIG. 3 for performing fallback from other PS networks toother CS networks are described below.

In a first step 113, a paging request for a CS voice call, originatingfrom an MSC (not shown), is sent to MME 112 with which UE 10 isregistered. The MME translates a Temporary Mobile Subscriber Identity(TMSI) associated with the paging request to the S-TMSI (serving TMSI)identifying UE 10. MME 112 may then page UE 10 using the S-TMSI. MME 112includes a ‘CS domain indicator’ in the paging request to notify UE 10that the paging request originates from the CS domain. Note that step113 occurs in the case of a UE-terminated call and does not occur in thecase of a UE-originated call.

Steps 116 a-116 d establish an RRC connection to the E-UTRAN cell onwhich UE 10 was camped. In step 116 c, UE 10 sends an RRC ConnectionSetup Complete message to access device 114. The RRC Connection SetupComplete message may carry a Non-Access Stratum (NAS) Extended ServiceRequest message, which may then be forwarded in step 116 d from accessdevice 114 to MME 112.

In step 118 an S1 context setup message is transmitted from MME 112 toaccess device 114 to transfer UE 10 context information. The contextsetup message may include an indication that CS fallback has beentriggered. In step 120 a, access device 114 transmits a Security ModeCommand message to start Access Stratum (AS) security. In step 120 b, UE10 sends a Security Mode Complete message to confirm the establishmentof integrity protection.

In step 122 a, access device 114 initiates an RRC ConnectionReconfiguration procedure to setup the radio bearers to be used inactive mode. In step 122 b, UE 10 sends an RRC ConnectionReconfiguration Complete message to confirm the completion of theprocedure. Additionally, as CS fallback has been triggered, accessdevice 114 may use the message in step 122 a, i.e., RRC ConnectionReconfiguration, to configure UE 10 to perform measurements on GERANcells and to configure measurement gaps in which UE 10 should performthose measurements. Exemplary measurement gap patterns are illustratedin FIG. 2 . In step 124, after receiving the measurement gap informationin step 122, UE 10 performs measurements on GERAN cells according to themeasurement configuration and measurement gaps.

In step 126, after detecting and measuring at least one GERAN cell, UE10 transmits a measurement report to access device 114. The measurementreport may optionally contain measurements for more than one GERAN cellif more than one potential cell is detected.

After receiving the measurement report, access device 114 sends an RRCcommand called Mobility from E-UTRA Command in step 128 to instruct UE10 to change to a particular GERAN cell. The RRC command may alsoinclude Network Assisted Cell Change (NACC) information (e.g., systeminformation) applicable to the identified GERAN cell. In one aspect, theidentified cell is selected from a list of appropriate GERAN cellsidentified in the measurement report transmitted by UE 10 in step 126.

In step 130, UE 10 selects the identified target GERAN cell, andacquires any system information, if not contained in the RRC command,that is necessary to transfer to the target GERAN cell. The acquisitionof system information for the target cell, however, may significantlydelay the CS fallback procedure. For example, it may take the UE two ormore seconds to acquire all the necessary system information to performCS fallback to a target GERAN cell, and 640 ms to read the necessarysystem information from a target UTRAN cell. In poor channel conditions,the UE may have to make multiple attempts to successfully retrieve thesystem information, further extending the delay.

Finally, in step 132, UE 10 initiates CS signaling on the GERAN cell toBase Station Subsystem (BSS) 134, which may comprise a base stationcontroller (BSC) and base transceiver station (BTS), to complete theanswer to paging (in the case of a UE-terminated call) or to originate acall (in the case of a UE-originated call).

As described above, FIG. 3 illustrates a message sequence forimplementing CS fallback to a GERAN cell. Depending upon theconfigurations of the original PS network and the target CS network,several of the steps illustrated in FIG. 3 may be modified. For example,when implementing CS fallback to GERAN using a PS handover, steps 128and 130 may be replaced with an inter-RAT PS handover to GERANprocedure. Also, when performing CS fallback to UTRAN, steps 128 and 130may be replaced with an inter-RAT PS handover to UTRAN procedure.

When a PS handover to the target cell is not supported, the accessdevice may trigger an inter-RAT cell change procedure by issuing a CellChange Order (CCO) in a Mobility From E-UTRA Command to UE 10 during anRRC connection. The inter-RAT CCO optionally includes NACC information,e.g., the system information of the target cell, and may contain a CSFallback Indicator that indicates to the UE that the CCO is triggered asa result of a CS fallback request. If the inter-RAT CCO contains a CSFallback Indicator and the UE fails to establish a connection to thetarget RAT, then the UE may presume that CS fallback has failed. The RRCconnection between UE 10 and E-UTRA is released when the cell changeprocedure is completed successfully.

When, for example, neither PS handover nor inter-RAT cell change aresupported by the RAT of the target cell (for example, GERAN or UTRAN),the access device 114 may trigger the CS fallback through redirectionby, for example, sending UE 10 an RRC Connection Release messagecontaining redirection information which may be an indication of thetarget RAT possibly together with an indication of a carrier frequencyor frequencies on that target RAT. The UE 10 may use the redirectioninformation in selecting a cell of the target RAT at step 130 and thenaccess the CS services on the selected cell at step 132.

When performing CS fallback to GERAN A/Gb mode, the UE may establish aradio resource connection using the procedures specified in 3GPP TS44.018 v.8.4.0. The UE requests and is assigned a dedicated channel.After the CS resources are allocated in the GERAN cell, and the mainsignaling link is established as described in 3GPP TS 44.018, the UE mayenter either Dual Transfer Mode (DTM) possibly requiring support of DTMby both the UE and the new cell or Dedicated Mode and the CS callestablishment procedure can take place.

If the MSC serving the GERAN or UTRAN cell is different from the MSCwith which the UE was registered when the UE was camped in E-UTRAN, theMSC serving the GERAN or UTRAN cell may reject the requested service. Inthat case, the UE may perform a Location Update procedure to inform thenew MSC of its location or may perform a combined Routing Area/LocationArea (RA/LA) update procedure to create an association between the (new)MSC and the SGSN (Serving GPRS Support Node) and to release the existingassociation between the (old) MSC and the MME.

In the case of UE-terminated calls, paging information may be sent tothe MME from the MSC that includes location information necessary topage the UE. The paging information may be sent to one or more networkaccess devices. Upon receiving the paging information, the UE mayestablish an RRC connection and send an Extended Service Request messagewith CS fallback indicator to the MME. The MME may then send parametersto the access device to request the access device to move the UE to thespecified UTRAN or GERAN cell.

In one aspect, the access device requests measurement reports from UE 10to determine the appropriate target cell for UE 10. The access devicemay then trigger an inter-RAT handover to the UTRAN or GERAN, aninter-RAT cell change to the GERAN, or a redirection procedure using,for example, the same mechanisms as described above in FIG. 3 . If theLA and/or RA information of the new cell is different from that storedin the UE, the UE may perform a combined RA/LA update procedure if thetarget system operates in Network Mode of Operation 1 or a Location AreaUpdate (LAU) otherwise.

The UE may then transmit a paging response message to the MSC in the newRAT and enter either DTM or Dedicated Mode (if in GERAN) orRRC_CONNECTED mode (if in UTRAN) and the CS call establishment procedurecompletes. If the UE is still in UTRAN/GERAN after the CS voice call isterminated, and if an LAU or a combined RA/LA update has not alreadybeen performed in the call establishment phase, then the UE may performeither an LAU or the combined RA/LA update procedure.

When UE 10 is in idle mode, UE 10 may be configured to periodicallyperform idle mode measurements for the purpose of cell reselection.During idle mode measurements, the UE detects candidate cells andmeasures signal strengths. As such, when UE 10 enters connected mode(e.g., steps 116 a-116 d of FIG. 3 ), UE 10 may already have detectedand performed measurements on one or more candidate GERAN cells. In oneaspect, UE 10 may be configured to store idle mode measurement resultsassociated with detected GERAN cells and later retrieve and use the idlemode measurements when performing CS fallback. The idle modemeasurements may replace or speed up connected mode measurements (i.e.,step 124 of FIG. 3 ), thereby minimizing delay in establishing thefallback service.

According to one set of E-UTRA specifications, for example, idle modemeasurements may be performed by UE 10 based on system information. Forexample, System Information Block Type 7 may include GERAN frequenciesand allowed network color codes used in the registered PLMN that may bemeasured by UE 10 while in idle mode. If the system information is notprovided, however, UE 10 may instead rely on UE 10's stored knowledge ofallocated GERAN frequencies and allowed network color codes used in theregistered PLMN to capture idle mode measurements.

In a first implementation of the present system that uses idle modemeasurement data captured by UE 10, the message sequence of FIG. 3 islargely unchanged. However, UE 10 is configured to store and retrieveidle mode measurement data. When access device 114 configures orrequests UE 10 to perform GERAN measurements at steps 122 a-122 b ofFIG. 3 in connected mode, UE 10 may then respond to the request with theidle mode measurement data rather than actively detect available GERANcells. Alternatively, should UE 10 undertake connected mode measurementsas in step 124 of FIG. 3 , UE 10 can minimize the time duration of theconnected mode measurement process by using information of the networkcells detected during the idle mode measurements. For example, the UEmay tune only to those frequencies where the BCCH carrier of allowedGERAN cells was detected during the idle mode measurements. As a result.UE 10 may start measuring the GERAN cells sooner and report themeasurement results together with the previously identified BSICs (basestation identity codes) as soon as sufficient measurements have beentaken. In either alternative, UE 10 may report measurement results toaccess device 114 upon request from access device 114.

This approach may be implemented by UE 10 without any changes (or onlyminimal changes) to existing specifications and may be implicitlyrequired by setting particular performance requirements (e.g. setting amaximum value for any delay associated with sending the measurementreport) or may be mandated such as by explicit requirements defined in aspecification.

Alternatively, when using idle mode measurements for CS fallback, newsignaling may be added to the message sequence of FIG. 3 to enableaccess device 114 to specifically request idle mode measurements and forUE 10 to send idle mode measurements to access device 114. FIG. 4illustrates a message sequence for implementing CS fallback with theaddition of new signaling for transmitting idle-mode measurementrequests and data between UE 10 and access device 114.

In FIG. 4 , access device 114 transmits a message 140 to UE 10specifically requesting that UE 10 report measurements performed in idlemode. Access device 114 may request the idle mode measurements bysending an ‘idle mode measurement reporting configuration’ via systeminformation broadcast in step 140 as illustrated on FIG. 4 .Alternatively, access device 114 may include an ‘idle mode measurementrequest’ in the RRC Connection Setup message as illustrated by step 142in FIG. 4 . Although both steps are shown on FIG. 4 , they may beexecuted independently, with only one of steps 140 and 142 being used torequest idle mode measurements.

The request for idle mode measurement results, whether in the systeminformation or in the RRC Connection Setup message or in some othermessage, may include such additional information as connection qualitythreshold or signal strength threshold, so that UE 10 only needs toreport cells meeting those criteria. The request may also identifyparticular RATs so that UE 10 would only report measurement results ofnetwork cells using those particular RATs. The request may furtherspecify a maximum number of network cells for which UE 10 may reportidle mode measurements.

In response to a request for the idle mode measurement reports, UE 10sends the requested idle mode measurements to access device 114. UE 10may include an ‘idle mode measurement report’ in the RRC ConnectionSetup Complete message as shown in step 144 of FIG. 4 . Alternatively,UE 10 may transmit a separate RRC Measurement Report message after theRRC Connection Setup Complete message has been sent, i.e., after an RRCconnection has been established, as shown in step 146. Again, althoughboth steps are shown on FIG. 4 , they may be executed independently,with only one of steps 144 and 146 being used to transmit idle modemeasurements. Whether UE 10 should report the idle mode measurements inor after the RRC Connection Setup Complete message may be specified inthe request for idle mode measurements from the E-UTRAN.

The idle mode measurement report may identify the RAT of each networkcell measured during the idle mode, the signal strength of each measurednetwork cell such as the strength of the respective pilot signal, thephase information of each measured network cell, identification of thecarrier of each measured network cell, the carrier to noise ratio(Ec/No), and/or received signal code power (RSCP) of the common pilotchannel (CPICH_RSCP) in measured UTRAN cells, and may provide a list ofthe network cells measured during the idle mode, optionally grouped byRATs.

The UE may be configured to send idle mode measurement information onlyas part of a CS fallback procedure. Alternatively, the UE may beconfigured to send idle mode measurement information even in cases whenthe UE is establishing a connection to the E-UTRA cell for reasons otherthan CS fallback (for example when accessing the cell for PS services).Whether to send the idle mode measurement information in all cases oronly in the case of a CS fallback may be under the control of the accessdevice and configured in the UE by means of a parameter within the idlemode measurement reporting configuration or idle mode measurementrequest, which configuration or request may be provided, e.g., in thesystem information or in the RRC Connection Setup message.

In some cases UE 10 may not have recent measurements of GERAN cells. Ifso, a measurement report may not be sent to the network (e.g., in steps144 or 146 of FIG. 4 ), an empty report may be sent, or the measurementreport may include an explicit indication that no measurements of GERANcells are available. In response, E-UTRAN (e.g., via access device 114of FIG. 4 ) may trigger connected mode measurement reporting to obtainthe measurements as illustrated by FIG. 3 .

Additionally, the idle mode measurements of GERAN cells may not berecent (for example, not received within the last minute) or outdated ifUE 10 is in a high mobility state (i.e. fast moving). In that case, UE10 may include in the measurement report an indication that the idlemode measurements are not very recent (e.g. stale), that the UE is fastmoving, or that the measurement report may not be particularly reliable.In response to an indication that the idle mode measurement data may notbe reliable, access device 114 may trigger connected mode measurementreporting to obtain more up-to-date measurements from UE 10, for exampleas illustrated in step 124 of FIG. 3 .

It may be preferable that the sending of any such idle or connected modemeasurement reports by UE 10 be under control of the network. Forexample, in some deployment scenarios where the coverage of a smallE-UTRAN cell in a rural area is within the coverage of a single GERANcell, UE 10 will always be directed to the same GERAN cell. In thatcase, measurement data may be unnecessary—the E-UTRAN cell already knowsto which GERAN cell UE 10 would most likely be directed. In many cases,however, such as urban environments where there is a high density ofGERAN cells, measurement reports generated by UE 10 enable the networkto select the most appropriate cell for a particular UE.

After receiving the information contained in the idle mode measurementreport, access device 114 may send an RRC Mobility from E-UTRA commandto instruct UE 10 to fallback to one of the GERAN cells reported by UE10 in the idle mode measurement report. As such, steps 124 and 126 ofFIG. 3 may not be executed and are thus not shown in FIG. 4 .Ultimately, however, access device 114 may make the determination as towhich GERAN cell UE 10 will be directed to. Accordingly, if accessdevice 114 determines that UE 10 should not be directed to any of thecells reported in the idle mode measurement report, access device 114may request in step 122 a that UE 10 perform active measuring andreporting of steps 124 and 126 of FIG. 3 in an attempt to findadditional candidate cells.

In another aspect, upon receiving a paging message or a request toinitiate a UE-originated call, UE 10 may select a GERAN cell based onprevious idle mode measurements without assistance from access device114. UE 10 may first signal access device 114 of the E-UTRAN cell beforeconnecting to the selected GERAN cell to carry out the call.Alternatively, UE 10 may directly connect to the selected GERAN cell tocarry out the call without any signaling to access device 114 of theE-UTRAN cell.

In some cases, to conserve UE power that may otherwise be used formaking idle measurements, certain conditions may be specified underwhich UE 10 does not perform measurements during idle mode. For example,in one particular implementation, idle measurements may not be made ifthe received power of the serving E-UTRAN cell is greater than apre-defined threshold, if E-UTRAN is assigned a higher priority thanGERAN, if combined attach fails, if the UE supports or prefers voicecall only through IMS (IP multimedia subsystem), and/or if IMS voicecall is available. Alternatively, UE 10 may determine whether to makeidle measurements based upon a combination of one or more factors suchas a) whether the serving E-UTRAN is known to not support particularservices such as voice (so that CS fallback may be necessary for voicecalls), b) whether the serving E-UTRAN is known to provide systeminformation for the target cell (in the manner of NACC making theacquisition of system information from the target RAT unnecessary), c)battery status of UE 10, and d) voice support of UE 10 (for example,laptop data cards may not support voice at all). If any such conditionsapply, UE 10 may not have any recent measurements of GERAN cells to beused after UE 10 enters connected mode. In that case. UE 10 may berequired to perform connected mode measurements as shown in the CSfallback process of FIG. 3 because idle mode measurements will not beavailable.

The following approaches may be implemented to increase the likelihoodthat UE 10 has available idle measurement information. First, UE 10 mayvoluntarily perform idle measurements on GERAN cells even when notmandated in view of the current operating conditions. Although thisoption may reduce the measurement delay associated with CS fallback, itmay negatively affect UE 10's power consumption. Second, UE 10 mayperform measurements on GERAN cells shortly after it has received thepaging message illustrated in step 113 of FIG. 3 for UE-terminatedcalls, or after receiving the request to initiate a UE-originated call,and before UE 10 enters connected mode. In that case, UE 10 may firstcontinuously perform sufficient GERAN measurements and only theninitiate the connection to the E-UTRAN cell (e.g., steps 116 a-116 d ofFIG. 3 ). Although this implementation may add some delay to the CSfallback procedure, the extra delay due to the short period ofcontinuous measurements will generally be less than the total delayassociated with performing the measurement during measurement gaps inconnected mode.

In addition to performing cell reselection measurements of GERAN cellswhile in idle mode, UE 10 may also attempt to acquire in advance systeminformation of the GERAN cells or other CS network cells that are mostlikely to be used in the case of CS fallback to shorten the CS fallbackprocess. For example, UE 10 may be configured to acquire systeminformation of the strongest GERAN neighbor cell while in idle mode.Then UE 10 may not need to retrieve the same system information duringthe CS fallback procedure as in, for example, step 130 of the sequenceof FIG. 3 , and can use the previously acquired system information tospeed up the fallback process.

UE 10 may be further configured to implement appropriate logic todetermine whether to acquire system information for one or more neighborcells while in idle mode. For example, the determination may depend ona) whether the serving E-UTRAN is known to not support particularservices such as voice (so that CS fallback may be necessary for voicecalls), b) whether the serving E-UTRAN is known to provide systeminformation for the target cell (in the manner of NACC making theacquisition of system information from the target RAT unnecessary), c)battery status of UE 10, d) voice support of UE 10 (for example, laptopdata cards may not support voice at all), e) number of detected cells(system information for a high number of cells requiring more time andbattery power to receive and decode, and a high number of cells makingit more likely that the eventual target cell will be one for which theUE has not yet acquired system information) or any combination of these.By limiting the circumstances under which UE 10 will attempt to acquiresystem information, battery consumption for UE 10 may be reducedcompared to a process whereby such neighbor cell system information isalways received and decoded.

In addition to minimizing occurrences of connected mode measurements byusing idle mode measurement data, the present system may be made moreefficient by further minimizing the duration of any connected modemeasurements that must be collected. In many cases, significant delayassociated with connected mode measurements may result from the use ofmeasurement gap patterns that give only a limited amount of time for UE10 to perform connected mode measurements, for example, as shown in FIG.2 .

In one aspect, UE 10 may be configured to dedicate more time toconnected mode measurements than are allocated by the existingmeasurement gap patterns described above (such as illustrated in FIG. 2.) In the CS fallback message sequence of FIG. 3 , for example, there isno ongoing voice call or data activity at the time of initiating the CSfallback process because UE 10 has just left idle mode. As such, UE 10may implement an enhanced measurement gap schedule to increase theamount of time UE 10 allocates to performing any required measurements.After UE 10 has performed sufficient measurements to detect one or morecandidate cells, UE 10 may cease the measurement process and send ameasurement report to access device 114.

FIG. 5 is an illustration of an exemplary measurement gap pattern thatmay be implemented by UE 10 for efficient measurements. In FIG. 5 , anRRC Connection Reconfiguration message is transmitted to begin themeasurement process in step 150. A single contiguous measurement gap 152is then defined during which UE 10 performs measurements for GERANcells. After UE 10 has detected one or more candidate cells, UE 10transmits the measurement results to the access device (e.g., an E-UTRANeNB) in step 154. Note that in the present implementation, even if anongoing data session is active, the CS fallback process may still bemore efficient using a longer and continuous measurement gap asillustrated in FIG. 5 instead of smaller distributed gaps as shown inFIG. 2 .

Although FIG. 5 illustrates a single contiguous period of time duringwhich UE 10 may perform measurements, efficiency may be optimized withvariations of the gap pattern illustrated in FIG. 2 , e.g., to definelonger or extended but still distributed measurement gaps.

In some cases, the radio coverage of an E-UTRAN or other PS network cellmay be entirely within the radio coverage of a single GERAN, UTRAN, orother CS network cell. In such a case, the provision of measurementreports by UE 10 to access device 114 may be unnecessary because accessdevice 114 may direct UE 10 to the overlapping CS network cell withoutrequiring any additional measurement information from UE 10. Sometimesthere may be more than one GERAN, UTRAN, or CS network cell that hasoverlapping radio coverage with the E-UTRAN or other PS network cell. Inthat case it may be sufficient that there exists at least one CS networkcell whose radio coverage is equal to or a superset of the radiocoverage of the E-UTRAN cell—the access device may direct UE 10 to anyof the overlapping GERAN cells without requesting measurement data fromUE 10. In the case of a UE-terminated call, for example, whentransmitting the paging message, access device 114 may additionallytransmit (either within the paging message or as a separate transmissionor transmissions) an identity of a specific GERAN cell to which UE 10should move, and/or system information corresponding to the specificGERAN cell. This method need not be limited to the specific radiocoverage scenario described above, but may be beneficial in scenarioswhere i) indicating a single target cell is likely to result in fallbacksuccess in a high number of cases, ii) only one cell is available toprovide CS services (regardless of the coverage of that cell), or iii)the goal is simply to minimize configuration effort associated with theaccess device, regardless of the relative coverage.

Alternatively, the identity and system information of the target GERANcell may be included in the system information of the E-UTRAN cell orother PS network cell. For example, a CSFB System Information Block(SIB) may be added to the E-UTRAN cell's system information to carry aGERAN cell identity and the GERAN cell's system information. In thatcase, the CSFB SIB indicates that whilst camped on the E-UTRAN cell thecontents of the SIB shall be considered by the UE 10 for CS fallback. UE10 can use the CSFB SIB in several exemplary scenarios as follows:

a) UE 10 may be camped on an E-UTRAN cell in an RRC_IDLE state. If UE 10has to perform a UE-originated CS call using CS fallback, then UE 10 maymove to the cell indicated by the CSFB SIB and initiate a CS call usingthat network cell, without accessing the E-UTRAN cell.

b) UE 10 may be camped on an E-UTRAN cell in an RRC_IDLE state whenreceiving paging information indicating a CS fallback UE-terminatedcall. Upon receiving the paging information, UE 10 moves to the cellindicated by the ‘CSFB SIB’ and responds to the paging information onthe target cell.

Alternatively, an additional field may be added to the paging messagethat specifies ‘Use CSFB SIB’. In response to receiving the ‘Use CSFBSIB’ indication, UE 10 moves to the cell indicated by the ‘CSFB SIB’.If, however, the ‘Use CSFB SIB’ indication is not received, then UE 10may respond to the paging information as illustrated in FIG. 3 , therebyallowing, for example, the E-UTRAN to request idle or connected modemeasurements and decide to which cell to direct UE 10.

c) UE 10 may be connected to an E-UTRAN cell in an RRC_CONNECTED state.If UE 10 has to perform a UE-originated or UE-terminated CS call usingCS fallback, the Mobility From E-UTRA Command message need not providecomplete network assistance information such as the system informationof the target GERAN cell. Instead the Mobility From E-UTRAN Commandmessage may have a single field that indicates ‘Use CSFB SIB’. In thatcase, because UE 10 has already acquired the ‘CSFB SIB’ on that cell. UE10 moves to the target cell as if it has received complete networkassistance information in the handover message.

d) UE 10 may be connected to an E-UTRAN cell in an RRC_CONNECTED state.Upon receipt of paging information or a requirement to initiate aUE-originated call, UE 10 performs local release, and selects theindicated GERAN cell without the signaling in the E-UTRAN cell.

A similar process may be used in the case of a UE-originated call(including an emergency call) as soon as access device 114 is aware thatthe reason for the connection request is a CS fallback call.

If more than one RAT may potentially provide the fallback service (suchas a circuit-switched voice call), the system information of the E-UTRANor other PS network cell may identify one or more target cells for eachsuch RAT. Certain criteria, such as radio coverage, connection quality,etc., may be used in selecting the most likely fallback cells toidentify in the system information.

With E-UTRAN it is possible to connect a single E-UTRAN radio accessnetwork to more than one core network belonging to different operators.This allows those operators to share the running costs associated withthe radio access network. In such a case, the E-UTRAN cell willbroadcast the Public Land Mobile Network (PLMN) identity of each of theoperators and the UE may register to the core network of just one of theoperators or PLMNs. Although operators may share the E-UTRAN radioaccess network, they may not share their UTRAN, GERAN or other networksthat may be used for CS fallback, or may have different agreements withoperators of the UTRAN, GERAN or other networks that may be used for CSfallback. Hence, an operator that supports CS fallback from a sharedE-UTRAN radio access network may require that a mobile stationregistered with that operator perform CS fallback to a particular targetUTRAN cell, GERAN cell or other cell, which may be different from thetarget cell preferred by a second operator for mobiles registered withthat second operator when such mobiles perform CS fallback. In such acase, the CSFB System Information Block may identify multiple targetcells (which may be UTRAN, GERAN or other cells) and correspondingsystem information for those cells belonging to (or preferred by) eachof the operators sharing the E-UTRAN radio access network. When the UEperforms CS fallback using the information from the CSFB SIB, the UE mayselect a cell identified in the CSFB SIB corresponding to the operatoror PLMN with which the UE is currently registered.

Turning to FIG. 6 , an alternative message sequence for implementing CSfallback is illustrated. The process eliminates some of thecommunication steps between access device 114 and MME 112. The processillustrated in FIG. 6 is applicable to CS fallback to GERAN usinginter-RAT cell change (optionally with NACC information), and alsoapplicable to CS fallback using redirection to a GERAN, UTRAN or anothernetwork cell. The process may also be made applicable to CS fallback toUTRAN with the option of using inter-RAT cell change to UTRAN. Themessage sequence of FIG. 6 includes the following steps:

In a first step 113, a paging request for a CS voice call, originatingfrom an MSC (not shown), is sent to MME 112 with which UE 10 isregistered. This step is largely unchanged from that of FIG. 3 .Furthermore, as in the case illustrated in FIG. 3 , this step may notoccur in the case of a mobile-originated call.

Steps 116 a-116 c establish an RRC connection on the E-UTRAN cell onwhich UE 10 was camped. In the final sub-step 116 c, UE 10 sends an RRCConnection Setup Complete message to access device 114, but the messageis modified compared to that shown in FIG. 3 . For example, the NASmessage (NAS Extended Service Request) is omitted from the RRCConnection Setup Complete. The NAS message would ordinarily becommunicated to MME 112 and so is not required when there is nocommunication between access device 114 and MME 112.

The RRC Connection Setup Complete may include an indicator that the RRCConnection is being requested for the purpose of CS fallback. Theindication could also be implicit from the absence of an NAS message.The RRC Connection Setup Complete may also include some UE capabilityinformation such as a list of the RATs and bands supported by UE 10. Theamount of UE capability information provided to access device 114 may beless than the amount that would normally have to be known by accessdevice 114 for the purposes of providing PS services from access device114. In the sequence shown in FIG. 3 , for example, access device 114obtains UE capability information from MME 112 in the S1 context setupmessage at step 118 of FIG. 3 . In cases where there is no suchcommunication between access device 114 and MME 112, as illustrated inFIG. 6 , the UE capability information or some subset of the UEcapability information may be provided by UE 10 over the radiointerface. Accordingly, in FIG. 6 , there is no S1 context messagecommunicated from MME 112 to access device 114. In FIG. 6 , a SecurityMode Command message to initiate AS integrity protection may be omittedcompared to the message sequence illustrated in FIG. 3 , becausesecurity context information such as security keys required for ASintegrity protection must be received from the MME, and there is nocommunication between MME 112 and access device 114.

In the example shown in FIG. 6 , RRC Connection Reconfiguration steps162 a and 162 b are modified as compared to the sequence of FIG. 3 .Steps 162 a and 162 b do not establish user plane radio bearers, whichmay only be established on request of the MME 112.

Steps 124, 126, 128 and 130 may be generally the same as those of FIG. 3. Some standard specifications may require that the RRC Mobility fromE-UTRA Command message be sent with integrity protection which impliesthat the message can only be sent after a Security Mode Command messagehas already been transmitted. This requirement may be lifted so thatwhen undertaking CS fallback the RRC Mobility from E-UTRA Commandmessage can be sent without integrity protection. As a result, step 128of FIG. 6 may be modified.

In an example involving emergency calls, UE 10 may be in idle modecamped on an E-UTRAN cell and not be registered with a CS network cell(e.g., UE 10 has not successfully performed a combined attachprocedure). If so, emergency calls may not be supported on the E-UTRANand UE 10 needs to move to a UTRAN or GERAN cell to initiate anemergency CS voice call. UE 10 may include an ‘emergency call’ causevalue in the RRC Connection Request message. Additionally, an ‘emergencyCSFB request indicator’ may be included in the RRC Connection SetupComplete message. As mentioned above, in this emergency CS fallbackscenario, the RRC messages may have to be sent without integrityprotection. In the alternative, UE 10 may directly re-select a UTRAN orGERAN cell to initiate the emergency CS voice call without signaling theE-UTRAN cell.

In one specific implementation, as may be required by 3GPP TS 23.272,subclause 7.7, when a request for a mobile-terminated service arrives inthe network, the MSC sends a paging message via SGSN to the MME. The MMEpages in the tracking areas (TAs) where UE 10 is registered, and alsorequests via the S3 interface of the SGSN that has an Idle modeSignaling Reduction (ISR) relation with the MME to page UE 10 in the RA.When UE 10 receives the paging by the MME, UE 10 may reselect a cell ofthe CS network with which the UE is registered and respond to the pagingby the SGSN to avoid Extended Service Request procedure and thesubsequent cell change procedure. FIG. 7 illustrates a communicationflow diagram for handling a UE-terminated call when ISR is active.

Referring to FIG. 7 , in steps 170 to 176 a UE-terminated call arrivesin MSCNLR 188 and the CS paging message is forwarded to MME 112. Insteps 178 a and 178 b MME 112 sends the CS paging message to each accessdevice 114 serving the TAs to which UE 10 is registered.

In step 182, upon receipt of the CS paging information, UE 10 reselectsa cell under the routing area (RA) with which UE 10 is currentlyregistered if ISR is active. To realize faster inter-RAT reselection, UE10 may use measurements and any system information of candidate cells(in particular to ensure that the cell of which reselection is performedbelongs to the same RA with which the UE 10 is registered). Meanwhile,in steps 180 a-180 c, MME 112 forwards the CS paging information to theassociated SGSN 190 if ISR is active and SGSN 190 pages the mobile inthe RA with which UE 10 is registered. Finally, in step 184, UE 10receives the CS paging information from steps 180 a-180 c and respondsto establish a UE-terminated call. This approach may be particularlybeneficial in cases where the core network operates in Network Mode ofOperation (NMO) 1.

In some cases, during CS fallback, UE 10 may be directed to a GERAN cellhaving a different LA from the LA in which UE 10 was registered whencamped on the E-UTRAN or another PS network. FIG. 8 illustrates such anexample. As shown in FIG. 8 , UE 10 is located close to the boundariesof the radio coverage of GERAN cells 204 and 206. GERAN cells 204 and206 are respectively associated with MSCs 208 and 210 and respectivelyhave LAs A and B. UE 10 is camped on E-UTRAN cell 202 which isassociated with LA A. Thus, when UE 10 performs the combinedregistration, such as combined attach or combined tracking area update,via the E-UTRAN cell, UE 10 becomes registered in LA A under MSC 208.

When a UE-terminated CS call arrives in MSC 208, the paging messagetakes the route through MME 112, access device 114, and E-UTRAN cell 202to UE 10. However, if the CS fallback procedure directs UE 10 to GERANcell 206, for example because GERAN cell 206 was reported as thestrongest GERAN cell, the page response may take the route through GERANcell 206, through BSS 216 to MSC 210. As a result, the page responsewill return to MSC 208, which may result in call failure or other CSdomain service setup failure.

The problems associated with UE 10 being directed to a GERAN cellbelonging to the wrong LA may be mitigated by informing the E-UTRAN orother PS network of UE 10's current registered LA. That information ofthe current registered LA can then be used to direct UE 10 to a GERAN orother CS network cell having the same LA.

In one implementation of the present system, the identification of theLA in which UE 10 is registered is provided to access device 114 by MME112 through, for example, the S1 context setup message from MME 112 toaccess device 114 in step 118 of FIG. 3 . Alternatively, information ofthe current registered LA may be provided directly by UE 10. If providedby UE 10, the information of the current registered LA may betransmitted at any stage in the message sequence prior to access device114 sending the RRC Mobility from E-UTRA command in step 128. Forexample, any of the messages from UE 10 to access device 114 (includingthe RRC Connection Setup Complete or the RRC Measurement Report) may beconfigured to include the registered LA information. In particular, theregistered LA information may be included in the RRC Connection SetupComplete message in the case that measurement information, obtainedwhile UE 10 is in idle mode, is added to the RRC Connection SetupComplete.

Upon receiving the registered LA information from UE 10 and, optionally,upon receiving an RRC Measurement Report from UE 10 that contains morethan one GERAN cell, access device 114 may select a GERAN cell thatbelongs to the registered LA for UE 10. After selecting the GERAN cell,access device 114 identifies that GERAN cell in a message to UE 10, suchas the RRC Mobility from E-UTRA command or the RRC Connection Releasemessage. Access device 114 may also provide the system information ofthe GERAN cell in such a message. As a result, UE 10 transfers to aGERAN cell having the same LA as the LA in which UE 10 is registered. Insome cases, access device 114 will use additional criteria in theselection of a suitable cell for CS fallback, for example, access device114 may only select from cells that have signal strength greater than agiven threshold. In some cases, different signal strength thresholds maybe defined for normal versus emergency calls.

The present system may also be configured for network deploymentscenarios where a single MSC controls multiple LAs. In such adeployment, it may be possible that a paging response reaches thecorrect MSC, even if it is sent via a cell having an LA different fromthe LA in which the UE is registered, if the different LA and theregistered LA are both managed by the same MSC. In such a case, accessdevice 114 may take into account this network configuration and considermultiple LAs when determining which target GERAN cell to direct UE 10towards in order to maximize the probability of fallback success. MME112 may also identify the LA in which UE 10 is registered, either fromsystem knowledge or from a message received from UE 10, and provide theidentity of the LA in which UE 10 is registered to access device 114 tofacilitate the selection of target cells.

In another implementation, the E-UTRAN may identify more than one targetcell for UE 10 to select from. In addition or in the alternative, theE-UTRAN may provide system information of the more than one cell to UE10. Such identifications or system information of the more than oneGERAN cell may be included in a message to UE 10 to release theconnection between UE 10 and the E-UTRAN access device. For example, theRRC Mobility from E-UTRA Command message may be modified to identifymore than one GERAN cell, may identify the carrier frequencies of themore than one GERAN cell, and may include system information for themore than one GERAN cell. Upon receiving the message from the E-UTRANidentifying more than one GERAN cell, UE 10 selects one of theidentified GERAN cells that belongs to the LA in which UE 10 iscurrently registered. To determine which of the included GERAN cellsbelong to the registered LA, UE 10 may inspect any available systeminformation applicable to the cells, obtained either from NACCinformation, i.e., the system information of the target cells includedin the message from the E-UTRAN, or from reading the system informationdirectly from the cells. In addition or in the alternative, UE 10 mayselect one of the identified GERAN cells based on previous idle modemeasurements.

The present system may also be configured for network deploymentscenarios where a single MSC controls multiple location areas. In thatcase, UE 10 may be additionally configured to prefer cells having adifferent LA but which are managed by the same MSC over those cellsmanaged by different MSCs.

UE 10 may also be configured to be aware of the LA of candidate GERANcells prior to reporting idle or connected mode measurements. In thatcase, UE 10 may apply a filtering or biasing rule to preferentiallyreport available cells of the same LA in which UE 10 is currentlyregistered. This may maximize the probability that access device 114selects a target cell which is in the same LA as that in which UE 10 iscurrently registered. In performing filtering or biasing, UE 10 may takeinto account an awareness of which of multiple LAs are served by thesame MSC so as to maximize the possibility that access device 114selects a target cell whose LA is the same as that in which UE 10 iscurrently registered, or whose LA is managed by the same MSC as thatwith which UE 10 is currently registered.

In conventional network implementations, the target system (i.e. the onethat provides the CS service) may not be aware that the call being setupresults from a CS fallback procedure. If the target system were to beaware that the call results from CS fallback, however, the time requiredfor call establishment via CS fallback may be reduced. Depending uponthe network configuration, the target system may be made aware of the CSfallback status of a call either by the UE or, in the case of a PShandover, by means of preparation phase signaling (for example, in thecase of fallback from an E-UTRA cell to a GERAN cell). In particular,the UE may indicate in a connection setup message, such as an RRCconnection request message or an RRC connection setup complete message,to the target system that the connection is a fallback connection toobtain a CS fallback service. Alternatively, the E-UTRA cell may informthe GERAN cell that the UE is seeking a fallback connection with theGERAN cell, and may do so by signaling from the eNB associated with theE-UTRA cell or signaling from the MME associated with the E-UTRA cell.

When the target cell is aware of the purpose of the connection requestfrom the UE, the target cell may permit the UE to go through anexpedited access procedure to receive an assignment of dedicatedchannels. The expedited access procedure is in contrast with a normalaccess procedure a mobile device needs to go through when establishing aconnection with the target cell other than a fallback connection.Compared to the normal access procedure, an expedited access proceduremay require less signaling or fewer steps. For example, a mobile deviceperforming an expedited access procedure may be given higher priority.

Still taking GERAN as an example, to speed up call establishment inGERAN, a Traffic CHannel (TCH), instead of a stand-alone dedicatedcontrol channel (SDCCH), may be assigned in direct response to a callconnection request identified as a request for a fallback connection,thereby eliminating the otherwise necessary step of signaling on theSDCCH before assignment of TCH. After assigning the TCH, callestablishment signaling may be performed using Fast Associated ControlCHannel (FACCH) signaling associated with the TCH, rather than on theSDCCH. Alternatively, rather than execute Authentication and Cipheringprocedures in the target system as part of call setup, any necessaryparameters for Authentication and Ciphering may be sent as part of thehandover procedure (i.e., as a Cipher mode setting and RAND).

Call setup signaling over GSM, for example, may take place on either theFACCH (Fast Associated Control Channel) or the SDCCH (Stand AloneDedicated Control Channel). Usually the setup occurs on the SDCCH, afterwhich the network assigns UE 10 to a traffic channel on which speechframes are transferred.

FIG. 9 illustrates a conventional message flow for implementing callsetup on a CS network for a UE-terminated call using the SDCCH. In step300 a paging request is sent from the BSS/MSC to UE 10 via the PagingChannel (PCH). In step 302, in response to the paging request, UE 10transmits a channel request to BSS/MSC using Random Access CHannel(RACH) signaling. In step 304, an assignment message is transmitted fromBSS/MSC to UE 10 via Access Grant CHannel (AGCH) signaling. The rest ofthe call setup signaling in FIG. 9 occurs using the SDCCH. In steps306-314 paging responses, authentication processes and the cipher modeare setup in several communications between UE 10 and BSS/MSC. In steps316-320 the call is setup via SDCCH signaling. In steps 322-328 aconnection for the voice call is established using the FACCH signaling.Finally, in step 330, after the call is setup ongoing voicecommunication occurs between UE 10 and another UE through BSS/MSC usingTCH signaling.

In contrast. FIG. 10 illustrates a message flow for implementing callsetup on a CS network for a UE-terminated call using FACCH signaling.When FACCH signaling is used, UE 10 may immediately be assigned atraffic channel using AGCH signaling as illustrated by step 332 of FIG.10 , in place of the two step procedure described above (i.e. signalingfollowed by TCH). The assignment allocates resources on the TCH/Fdirectly making the second step unnecessary. In steps 334-344 FACCHsignaling is used to process the response to the paging request, setupthe call, and establish a connection. In step 346, ongoing voicecommunication occurs between UE 10 and another UE through BSS/MSC usingTCH signaling. FIG. 10 also illustrates optional step 348 involving achannel modify message sent using FACCH signaling from BSS/MSC to UE 10.This message may be set to UE 10 by the network (e.g., BSS/MSC) tospecify MultiRate Configuration Informational Element (IE) such as forspecifying AMR parameters.

It is important to note that FACCH is an in-band signaling channelcreated using resources that may otherwise be assigned to the TCH. Thein-band signaling approach (instead of the out-band signaling over SDCCHillustrated in FIG. 9 ) coupled with the removal of theAuthentication/Ciphering procedure, may reduce the overall call set-uptime. Unfortunately, one drawback of this approach is that there may beno option available (in the Immediate Assignment message) to indicatethe AMR speech coding option (i.e. MultiRate Configuration IE) earlieron in the call setup. This may be resolved, however, by the networksending the Channel mode Modify message after the call is connected.

There may be additional benefits if the target system is aware that thecall is a CS fallback call. For example, redirection back to E-UTRAN atcall termination may be applied to CS fallback calls. Because the mobilewas camped on E-UTRAN when the CS fallback process was initiated, it ismay be optimal that UE 10 be returned to and camp on an E-UTRAN cell,and possibly the original E-UTRAN cell. To do so, the GERAN cell may, atthe release of fallback connection with UE 10, indicate to UE 10 that UE10 should be redirected to and re-select an E-TRAN cell. The indicationmay identify the E-UTRAN or the original E-UTRAN cell, and may evencontain system information of the original E-UTRAN cell. Alternatively,UE 10 may store the identity of the E-UTRAN or the original E-UTRAN celland/or the system information of the original UTRAN cell, therebyenabling a re-selection of the original E-UTRAN cell upon receiving theredirect indication from the GERAN cell. Also, appropriate settings ofpriorities for autonomous reselection may be configured for UE 10 toincrease the probability that it reselects to E-UTRAN following thecall. In particular, if UE 10 receives a higher priority of cellreselection to the E-UTRAN than to the GERAN, once the fallbackconnection with the GERAN cell is released, UE 10 may first look for anE-UTRAN cell and reselect it if one is found.

Referring now to FIG. 11 , a wireless communications system including anembodiment of an exemplary UE 10 is illustrated. The UE is operable forimplementing aspects of the disclosure, but the disclosure should not belimited to these implementations. Though illustrated as a mobile phone,the UE may take various forms including a wireless handset, a pager, apersonal digital assistant (PDA), a portable computer, a tabletcomputer, a laptop computer, smartphones, printers, fax machines,televisions, set top boxes, and other video display devices, home audioequipment and other home entertainment systems, home monitoring andcontrol systems (e.g., home monitoring, alarm systems and climatecontrol systems), and enhanced home appliances such as computerizedrefrigerators. Many suitable devices combine some or all of thesefunctions. In some embodiments of the disclosure, the UE 10 is not ageneral purpose computing device like a portable, laptop or tabletcomputer, but rather is a special-purpose communications device such asa mobile phone, a wireless handset, a pager, a PDA, or atelecommunications device installed in a vehicle. The UE 10 may also bea device, include a device, or be included in a device that has similarcapabilities but that is not transportable, such as a desktop computer,a set-top box, or a network node. The UE 10 may support specializedactivities such as gaming, inventory control, job control, and/or taskmanagement functions, and so on.

The UE 10 includes a display 702. The UE 10 also includes atouch-sensitive surface, a keyboard or other input keys generallyreferred to as 704 for receiving input by a user. The keyboard may be afull or reduced alphanumeric keyboard such as QWERTY, Dvorak, AZERTY,and sequential types, or a traditional numeric keypad with alphabetletters associated with a telephone keypad. The input keys may include atrackwheel, an exit or escape key, a trackball, and other navigationalor functional keys, which may be inwardly depressed to provide furtherinput function. The UE 10 may present options for the user to select,controls for the user to actuate, and/or cursors or other indicators forthe user to direct.

The UE 10 may further accept data entry from the user, including numbersto dial or various parameter values for configuring the operation of theUE 10. The UE 10 may further execute one or more software or firmwareapplications in response to user commands. These applications mayconfigure the UE 10 to perform various customized functions in responseto user interaction. Additionally, the UE 10 may be programmed and/orconfigured over-the-air, for example from a wireless base station, awireless access point, or a peer UE 10.

Among the various applications executable by the UE 10 is a web browser,which enables the display 702 to show a web page. The web page may beobtained via wireless communications with a wireless network accessnode, a cell tower, a peer UE 10, or any other wireless communicationsnetwork or system 700. The network 700 is coupled to a wired network708, such as the Internet. Via the wireless link and the wired network,the UE 10 has access to information on various servers, such as a server710. The server 710 may provide content that may be shown on the display702. Alternately, the UE 10 may access the network 700 through a peer UE10 acting as an intermediary, in a relay type or hop type of connection.

FIG. 12 shows a block diagram of the UE 10. While a variety of knowncomponents of UE 10 are depicted, in an embodiment a subset of thelisted components and/or additional components not listed may beincluded in the UE 10. The UE 10 includes a digital signal processor(DSP) 802 and a memory 804. As shown, the UE 10 may further include anantenna and front end unit 806, a radio frequency (RF) transceiver 808,an analog baseband processing unit 810, a microphone 812, an earpiecespeaker 814, a headset port 816, an input/output interface 818, aremovable memory card 820, a universal serial bus (USB) port 822, ashort range wireless communication sub-system 824, an alert 826, akeypad 828, a liquid crystal display (LCD), which may include a touchsensitive surface 830, an LCD controller 832, a charge-coupled device(CCD) camera 834, a camera controller 836, and a global positioningsystem (GPS) sensor 838. In an embodiment, the UE 10 may include anotherkind of display that does not provide a touch sensitive screen. In anembodiment, the DSP 802 may communicate directly with the memory 804without passing through the input/output interface 818.

The DSP 802 or some other form of controller or central processing unitoperates to control the various components of the UE 10 in accordancewith embedded software or firmware stored in memory 804 or stored inmemory contained within the DSP 802 itself. In addition to the embeddedsoftware or firmware, the DSP 802 may execute other applications storedin the memory 804 or made available via information carrier media suchas portable data storage media like the removable memory card 820 or viawired or wireless network communications. The application software maycomprise a compiled set of machine-readable instructions that configurethe DSP 802 to provide the desired functionality, or the applicationsoftware may be high-level software instructions to be processed by aninterpreter or compiler to indirectly configure the DSP 802.

The antenna and front end unit 806 may be provided to convert betweenwireless signals and electrical signals, enabling the UE 10 to send andreceive information from a cellular network or some other availablewireless communications network or from a peer UE 10. In an embodiment,the antenna and front end unit 806 may include multiple antennas tosupport beam forming and/or multiple input multiple output (MIMO)operations. As is known to those skilled in the art, MIMO operations mayprovide spatial diversity which can be used to overcome difficultchannel conditions and/or increase channel throughput. The antenna andfront end unit 806 may include antenna tuning and/or impedance matchingcomponents, RF power amplifiers, and/or low noise amplifiers.

The RF transceiver 808 provides frequency shifting, converting receivedRF signals to baseband and converting baseband transmit signals to RF.In some descriptions a radio transceiver or RF transceiver may beunderstood to include other signal processing functionality such asmodulation/demodulation, coding/decoding, interleaving/deinterleaving,spreading/despreading, inverse fast Fourier transforming (IFFT)/fastFourier transforming (FFT), cyclic prefix appending/removal, and othersignal processing functions. For the purposes of clarity, thedescription here separates the description of this signal processingfrom the RF and/or radio stage and conceptually allocates that signalprocessing to the analog baseband processing unit 810 and/or the DSP 802or other central processing unit. In some embodiments, the RFtransceiver 808, portions of the antenna and front end 806, and theanalog baseband processing unit 810 may be combined in one or moreprocessing units and/or application specific integrated circuits(ASICs).

The analog baseband processing unit 810 may provide various analogprocessing of inputs and outputs, for example analog processing ofinputs from the microphone 812 and the headset 816 and outputs to theearpiece 814 and the headset 816. To that end, the analog basebandprocessing unit 810 may have ports for connecting to the built-inmicrophone 812 and the earpiece speaker 814 that enable the UE 10 to beused as a cell phone. The analog baseband processing unit 810 mayfurther include a port for connecting to a headset or other hands-freemicrophone and speaker configuration. The analog baseband processingunit 810 may provide digital-to-analog conversion in one signaldirection and analog-to-digital conversion in the opposing signaldirection. In some embodiments, at least some of the functionality ofthe analog baseband processing unit 810 may be provided by digitalprocessing components, for example by the DSP 802 or by other centralprocessing units.

The DSP 802 may perform modulation/demodulation, coding/decoding,interleaving/deinterleaving, spreading/despreading, inverse fast Fouriertransforming (IFFT)/fast Fourier transforming (FFT), cyclic prefixappending/removal, and other signal processing functions associated withwireless communications. In an embodiment, for example in a codedivision multiple access (CDMA) technology application, for atransmitter function the DSP 802 may perform modulation, coding,interleaving, and spreading, and for a receiver function the DSP 802 mayperform despreading, deinterleaving, decoding, and demodulation. Inanother embodiment, for example in an orthogonal frequency divisionmultiplex access (OFDMA) technology application, for the transmitterfunction the DSP 802 may perform modulation, coding, interleaving,inverse fast Fourier transforming, and cyclic prefix appending, and fora receiver function the DSP 802 may perform cyclic prefix removal, fastFourier transforming, deinterleaving, decoding, and demodulation. Inother wireless technology applications, yet other signal processingfunctions and combinations of signal processing functions may beperformed by the DSP 802.

The DSP 802 may communicate with a wireless network via the analogbaseband processing unit 810. In some embodiments, the communication mayprovide Internet connectivity, enabling a user to gain access to contenton the Internet and to send and receive e-mail or text messages. Theinput/output interface 818 interconnects the DSP 802 and variousmemories and interfaces. The memory 804 and the removable memory card820 may provide software and data to configure the operation of the DSP802. Among the interfaces may be the USB interface 822 and the shortrange wireless communication sub-system 824. The USB interface 822 maybe used to charge the UE 10 and may also enable the UE 10 to function asa peripheral device to exchange information with a personal computer orother computer system. The short range wireless communication sub-system824 may include an infrared port, a Bluetooth interface, an IEEE 802.11compliant wireless interface, or any other short range wirelesscommunication sub-system, which may enable the UE 10 to communicatewirelessly with other nearby mobile devices and/or wireless basestations.

The input/output interface 818 may further connect the DSP 802 to thealert 826 that, when triggered, causes the UE 10 to provide a notice tothe user, for example, by ringing, playing a melody, or vibrating. Thealert 826 may serve as a mechanism for alerting the user to any ofvarious events such as an incoming call, a new text message, and anappointment reminder by silently vibrating, or by playing a specificpre-assigned melody for a particular caller.

The keypad 828 couples to the DSP 802 via the interface 818 to provideone mechanism for the user to make selections, enter information, andotherwise provide input to the UE 10. The keyboard 828 may be a full orreduced alphanumeric keyboard such as QWERTY, Dvorak, AZERTY andsequential types, or a traditional numeric keypad with alphabet lettersassociated with a telephone keypad. The input keys may include atrackwheel, an exit or escape key, a trackball, and other navigationalor functional keys, which may be inwardly depressed to provide furtherinput function. Another input mechanism may be the LCD 830, which mayinclude touch screen capability and also display text and/or graphics tothe user. The LCD controller 832 couples the DSP 802 to the LCD 830.

The CCD camera 834, if equipped, enables the UE 10 to take digitalpictures. The DSP 802 communicates with the CCD camera 834 via thecamera controller 836. In another embodiment, a camera operatingaccording to a technology other than Charge Coupled Device cameras maybe employed. The GPS sensor 838 is coupled to the DSP 802 to decodeglobal positioning system signals, thereby enabling the UE 10 todetermine its position. Various other peripherals may also be includedto provide additional functions, e.g., radio and television reception.

FIG. 13 illustrates a software environment 902 that may be implementedby the DSP 802. The DSP 802 executes operating system drivers 904 thatprovide a platform from which the rest of the software operates. Theoperating system drivers 904 provide drivers for the UE hardware withstandardized interfaces that are accessible to application software. Theoperating system drivers 904 include application management services(“AMS”) 906 that transfer control between applications running on the UE10. Also shown in FIG. 13 are a web browser application 908, a mediaplayer application 910, and Java applets 912. The web browserapplication 908 configures the UE 10 to operate as a web browser,allowing a user to enter information into forms and select links toretrieve and view web pages. The media player application 910 configuresthe UE 10 to retrieve and play audio or audiovisual media. The Javaapplets 912 configure the UE 10 to provide games, utilities, and otherfunctionality. A component 914 might provide functionality describedherein.

The UE 10, access device 120, and other components described above mightinclude a processing component that is capable of executing instructionsrelated to the actions described above. FIG. 14 illustrates an exampleof a system 1000 that includes a processing component 1010 suitable forimplementing one or more embodiments disclosed herein. In addition tothe processor 1010 (which may be referred to as a central processor unit(CPU or DSP), the system 1000 might include network connectivity devices1020, random access memory (RAM) 1030, read only memory (ROM) 1040,secondary storage 1050, and input/output (I/O) devices 1060. In somecases, some of these components may not be present or may be combined invarious combinations with one another or with other components notshown. These components might be located in a single physical entity orin more than one physical entity. Any actions described herein as beingtaken by the processor 1010 might be taken by the processor 1010 aloneor by the processor 1010 in conjunction with one or more componentsshown or not shown in the drawing.

The processor 1010 executes instructions, codes, computer programs, orscripts that it might access from the network connectivity devices 1020,RAM 1030, ROM 1040, or secondary storage 1050 (which might includevarious disk-based systems such as hard disk, floppy disk, or opticaldisk). While only one processor 1010 is shown, multiple processors maybe present. Thus, while instructions may be discussed as being executedby a processor, the instructions may be executed simultaneously,serially, or otherwise by one or multiple processors. The processor 1010may be implemented as one or more CPU chips.

The network connectivity devices 1020 may take the form of modems, modembanks, Ethernet devices, universal serial bus (USB) interface devices,serial interfaces, token ring devices, fiber distributed data interface(FDDI) devices, wireless local area network (WLAN) devices, radiotransceiver devices such as code division multiple access (CDMA)devices, global system for mobile communications (GSM) radio transceiverdevices, worldwide interoperability for microwave access (WiMAX)devices, and/or other well-known devices for connecting to networks.These network connectivity devices 1020 may enable the processor 1010 tocommunicate with the Internet or one or more telecommunications networksor other networks from which the processor 1010 might receiveinformation or to which the processor 1010 might output information.

The network connectivity devices 1020 might also include one or moretransceiver components 1025 capable of transmitting and/or receivingdata wirelessly in the form of electromagnetic waves, such as radiofrequency signals or microwave frequency signals. Alternatively, thedata may propagate in or on the surface of electrical conductors, incoaxial cables, in waveguides, in optical media such as optical fiber,or in other media. The transceiver component 1025 might include separatereceiving and transmitting units or a single transceiver. Informationtransmitted or received by the transceiver 1025 may include data thathas been processed by the processor 1010 or instructions that are to beexecuted by processor 1010. Such information may be received from andoutputted to a network in the form, for example, of a computer databaseband signal or signal embodied in a carrier wave. The data may beordered according to different sequences as may be desirable for eitherprocessing or generating the data or transmitting or receiving the data.The baseband signal, the signal embedded in the carrier wave, or othertypes of signals currently used or hereafter developed may be referredto as the transmission medium and may be generated according to severalmethods well known to one skilled in the art.

The RAM 1030 might be used to store volatile data and perhaps to storeinstructions that are executed by the processor 1010. The ROM 1040 is anon-volatile memory device that typically has a smaller memory capacitythan the memory capacity of the secondary storage 1050. ROM 1040 mightbe used to store instructions and perhaps data that are read duringexecution of the instructions. Access to both RAM 1030 and ROM 1040 istypically faster than to secondary storage 1050. The secondary storage1050 is typically comprised of one or more disk drives or tape drivesand might be used for non-volatile storage of data or as an over-flowdata storage device if RAM 1030 is not large enough to hold all workingdata. Secondary storage 1050 may be used to store programs that areloaded into RAM 1030 when such programs are selected for execution.

The I/O devices 1060 may include liquid crystal displays (LCDs), touchscreen displays, keyboards, keypads, switches, dials, mice, track balls,voice recognizers, card readers, paper tape readers, printers, videomonitors, or other well-known input/output devices. Also, thetransceiver 1025 might be considered to be a component of the I/Odevices 1060 instead of or in addition to being a component of thenetwork connectivity devices 1020. Some or all of the I/O devices 1060may be substantially similar to various components depicted in thepreviously described drawing of the UE 10, such as the display 702 andthe input 704.

While several embodiments have been provided in the present disclosure,it should be understood that the disclosed systems and methods may beembodied in many other specific forms without departing from the spiritor scope of the present disclosure. The present examples are to beconsidered as illustrative and not restrictive, and the intention is notto be limited to the details given herein. The various elements orcomponents may be combined or integrated in another system or certainfeatures may be omitted, or not implemented. For example, although thepresent disclosure uses circuit-switched fallback as an example, thetechniques and methods described herein can be more generally applied insituations where UE attempts to access a service not available through acurrent network cell with which the UE is associated but availablethrough another network cell with which the UE is not currentlyassociated. The service may be unavailable to the UE through the currentnetwork cell, for example, if the current network cell does not supportthe service at all, or if the service is only available through thecurrent network cell under a protocol that is not compatible with theUE's capability. For example, in the situation where the UE attempts toaccess voice call and an E-UTRAN cell may provide voice call but onlythrough IP services, the service is unavailable through the E-UTRAN cellif the UE only supports circuit-switched voice call. Additionally, thecurrent network cell and the target network cell may or may not be inthe same network and may or may not use the same RAT. A network operatormay configure network cells in the same radio access network such that aparticular service may be provided in some of the network cells but notothers. Depending on where the service is provided, the current networkcell may direct the UE to a different radio access network using adifferent RAT, or to a different network cell in the same radio accessnetwork.

Also, techniques, systems, subsystems and methods described andillustrated in the various embodiments as discrete or separate may becombined or integrated with other systems, modules, techniques, ormethods without departing from the scope of the present disclosure.Other items shown or discussed as coupled or directly coupled orcommunicating with each other may be indirectly coupled or communicatingthrough some interface, device, or intermediate component, whetherelectrically, mechanically, or otherwise. Other examples of changes,substitutions, and alterations are ascertainable by one skilled in theart and could be made without departing from the spirit and scopedisclosed herein.

What is claimed is:
 1. A method performed by user equipment (UE),comprising: sending a request to access a service via a first networkcell associated with the UE, said first network cell part of a firstnetwork, the first network having a first radio access technology; andreceiving a message responsive to the request from an access deviceassociated with the first network, the message identifying a pluralityof second network cells capable of providing the service, said secondnetwork cells having a second radio access technology.
 2. The method ofclaim 1, wherein the service is circuit-switched voice.
 3. The method ofclaim 1, wherein the service is not provided by the first network cell.4. The method of claim 1 wherein the request to access the service is aNon-Access Stratum (NAS) extended service request message.
 5. The methodof claim 1, wherein the UE does not support a protocol under which thefirst network cell provides the service.
 6. The method of claim 1,further comprising: receiving user input in response to which the UEperforms the sending of the request to access the service.
 7. The methodof claim 1, further comprising: receiving a paging message from thefirst network cell in response to which the UE performs the sending ofthe request to access the service.
 8. The method of claim 1, wherein themessage contains system information of the plurality of second networkcells.
 9. The method of claim 1, wherein the message identifies locationareas of the plurality of second network cells.
 10. The method of claim9, further comprising: comparing a location area in which the UE isregistered with the location areas of the plurality of second networkcells; and selecting one of the plurality of second network cellsbelonging to the same location area as the location area in which the UEis registered.
 11. The method of claim 1, further comprising receivingsystem information of the plurality of second network cells identifiedin the message.
 12. The method of claim 11, wherein the systeminformation identifies location areas of the plurality of second networkcells, the method further comprising: comparing a location area (LA) inwhich the UE is registered with the location areas of the plurality ofsecond network cells; and selecting one of the plurality of secondnetwork cells based on the comparison.
 13. The method of claim 12,wherein the selecting comprises selecting one of the plurality of secondnetwork cells belonging to the same location area as the location areain which the UE is registered.
 14. The method of claim 1, wherein themessage directs the UE to connect to one of the plurality of secondnetwork cells.
 15. The method of claim 1, wherein the message directsthe UE to switch from the first network cell associated with the firstradio access technology to a second network cell associated with thesecond radio access technology.
 16. The method of claim 1, wherein themessage directs the UE to release a connection with the access device.17. The method of claim 16 wherein the message is a RRC ConnectionRelease message.
 18. The method of claim 1 wherein the first radioaccess technology is evolved universal terrestrial radio access, E-UTRA,and the access device is an evolved node B (eNB) associated with thefirst network cell.
 19. The method of claim 14, wherein the plurality ofsecond network cells are in one of a universal terrestrial radio accessnetwork (UTRAN), a global system for mobile communications (GSM)network, an evolution-data optimized (EV-DO) network, a 3GSM network, adigital enhanced cordless (DECT) network, a digital AMPS (IS-136/TDMA)network, an integrated digital enhanced network (iDEN), a universalmobile telecommunications system (UMTS), an enhanced data rates for GSMevolution (EDGE) network, a general packet radio service (GPRS) network,and a GPRS/EDGE radio access network (GERAN).
 20. A non-transitorycomputer-readable storage medium containing instructions that whenexecuted by a processor of a user equipment (UE) perform a method,comprising: sending a request to access a service via a first networkcell associated with the UE, said first network cell part of a firstnetwork, the first network having a first radio access technology; andreceiving a message responsive to the request from an access deviceassociated with the first network, the message identifying a pluralityof second network cells capable of providing the service, said secondnetwork cells having a second radio access technology.